In solid state laser oscillators and amplifiers (in a word, solid state lasers) the active medium or material comprises crystals or glasses in the form of rods and slabs.
Laser rods are conventionally shaped as longitudinally extending cylindrical elements having a circular or regular polygonal cross-sectional profile. Laser slabs are generally in the form of planar, square or rectangular elements or parallelepipeds.
Ions and atoms capable of fluorescence are incorporated in these materials. These ions or atoms are stimulated ("pumped") so that an electron population inversion between two energy levels exists, which is used for the laser emission. Pumping is generally done by gas discharge lamps, flash lamps, other lasers or also light emitting diodes. During the pumping, the active solid state laser materials are heated due to a variety of energy transfer effects. Due to this heating effect, the laser rods or slabs must be cooled when under conditions of high pumping in order to prevent their destruction. For this reason the laser rods or slabs are positioned in flowing coolants. In addition, with large pumping powers, very high temperature gradients occur in the rods or slabs as a result of which the quality of the laser beam becomes poorer, even at temperatures below the destruction threshold.
Because of these thermal loads the maximum attainable average powers of the solid state lasers are predetermined and their use possibilities are limited. From U.S. Pat. No. 3,297,957 and Swiss patent CH 597 701 it is known that grooves which encircle a laser rod normal to its axis can improve the overall efficiency of such a laser: The pumping efficiency can be increased and the detrimental effects of the whisper modes can be reduced. These grooves, however, do not improve the cooling of the active medium of the solid state lasers, which is the primary object of the present invention to be described in the following.